Member directory is empty for non-admins

We have defined a user role via code in our own plugin. This user role is displayed in the backend in the “user roles” list of ultimate member.

We set up a member directory to show this user group. When viewing the member directory as an administrator, the directory shows as expected.

When viewing the very same member directory as a user which is a member of this role, the member directory is empty.

What settings do we need to adjust, so the user role can view all other members in the member directory?

For the sake of completness this is our code for registering the user role:

register_activation_hook(__FILE__, 'add_network_member_role');

function add_network_member_role() {
    $capabilities = array(
        'read' => true,
        'upload_files' => true,
        'edit_network_post' => true,
        'read_network_post' => true,
        'delete_network_post' => true,
        'edit_network_posts' => true,
        'publish_network_posts' => true,
        'edit_others_posts' => false,
        'delete_others_posts' => false,
        'edit_others_network_posts' => false,
        'delete_others_network_posts' => false,
        'edit_published_network_posts' => true,
        'delete_published_network_posts' => true,
        'moderate_comments' => false,
        'edit_comments' => false,
        'delete_comments' => false,
        'edit_comment' => false,
        'delete_comment' => false,
        'list_users' => true,
    );

    add_role('network_member', 'Network Member', $capabilities);
}